Jeffrey Pine- -Mixed Conifer Forests Mixed Conifer Forests Jeffrey Pine in Northwestern Mexico in Northwestern Mexico Scott Stephens Department of Environmental Science, Policy, and Management UC Berkeley
Sierra San Pedro Martir Sierra San Pedro Martir Mountains Mountains Northern Baja California Mediterranean climate (more summer precipitation than most of CA.) Annual precipitation averages 24 in (61 cm) limited precipitation record Granitic parent material common Area has been grazed by livestock 200 years, varying intensities
Forests in Northwestern Mexico Forests in Northwestern Mexico Sierra San Pedro Martir (SSPM) Within the California floristic province – unique to Northern Baja California Forested area approximately 100,000 ac. Elevation upper plateau 8800 feet – 3 large plateaus, peninsular mountains Jeffrey pine-mixed conifer forests – Similar to forests in southern California and eastern Sierra Nevada Fire suppression begins in 1970, no harvesting
Image 1: Aerial Image 1: Aerial
FH Mission FH Mission
FRI 10% FRI 10%
Fire History Fire History • Frequency similar to Jeffrey pine dominated forests in the eastern Sierra Nevada and Lake Tahoe • Interval between fires 8-15 years • Seasonality of past fires is different than Sierra – Most fires in earlywood, June and July – Few in dormant period • Stephens et al. 2003
Forest Structure Sampling Forest Structure Sampling Jeffrey pine-mixed conifer forest 7 x 7 grid (200 m between plots) – Area sampled 512 acres (1.44 km 2 ) – Grid densification in random area • Spatial statistics being done Similar aspect, soils, slope, vegetation • Live tree plots 0.25 acre • Snag plots 1.0 acre
Forest Composition Forest Composition Jeffrey pine-mixed conifer forest (percent basal area by species) – 66.3% Jeffrey pine ( Pinus jeffreyi ) – 23.1% white fir ( Abies concolor ) – 8.4% sugar pine ( Pinus lambertiana ) – 1.4% lodgepole pine ( Pinus contorta ) – 0.8 % quaking aspen (Populus tremuloides) Average basal area 86 ft 2 /acre (20 m 2 /ha) range 25 - 218 ft 2 /acre (5.8-51 m 2 /ha)
Forest Structure Forest Structure Live trees (above 1 inch DBH) – Average 60 trees/acre (149 trees/ha) – Range 12 - 128 trees/acre Structural classification of forest (hierarchical cluster analysis ) – 33% old forest, single stratum – 24% young forest, multi-strata – 43% old forest, spatially distinct multi-strata Large amount of variability Stephens and Gill 2005
Regeneration in the SSPM Regeneration in the SSPM • Regeneration in distinct patches • What are the size and shapes of the patches? • What percentage of this forest is currently in patches?
Patch Definition Patch Definition • All areas with at least 3 trees 2.5-15 cm DBH within a 7m x 7m area (22.5 ft x 22.5 ft.) – Used information from 4 ha stem map • Line intercept method (random start) – Total distance 8.4 km (5.22 miles) – If patch intercepted then data taken
Patch Results Patch Results • Number of patches: 54 • Average patch size 0.026 acres (0.01ha) – Range .0025 – 0.17 acres (0.001-0.067 ha) • Average tree height in patch 19 ft (5.8 m) • Average tree height adjacent to patch 75.1 ft (22.9 m) • Percent of area in patches: 3.8% • Patch abundance (number/ha): 8.5 • Stephens and Fry (J. Veg Sci 2005)
Tree Ages Tree Ages • Mapped x and y location of every tree and seedling in two 10 acre areas • Cored every tree above 1 inch DBH – Cores taken approximately 6 inches above ground level • All corers crossdated • Pattern (spatial statistics) being investigated
Tree Age in 10 acre Stem Map Tree Age in 10 acre Stem Map (678 total) (678 total) 180 160 140 Number of Trees 120 100 80 60 40 20 0 1300 1400 1500 1600 1700 1800 1900 2000 Year
Snag Density Snag Density Snags (2001 and before) –average 1.7 snags/ac (4.2 snags/ha) –0 - 9 snags/ acre (0-22.5 snags/ha) Snags (2002) (added 22 more) –average 2.1 snags/acre (5.3 snags/ha) –0 - 9 snags/ acre (0-22.5 snags/ha) • Drought last 4 years, more mortality in 2003 Stephens 2004, Stephens et al. 2007
How Common are Average How Common are Average Snag Densities in the SSPM? Snag Densities in the SSPM? 0 snags on 26% of plots Less than average density on 65% of plots Greater than 4 snags/ac (10 snags/ha) in 14% of plots Conclusion – average densities are rare – occur in approximately 12% of plots
Surface and Ground Fuel Loads Surface and Ground Fuel Loads 3 fuel inventory transects at each plot (147 transects) Used van Wagtendonk’s data (1996, 1998) Average surface fuel load 6.6 tons/acre (15.2 metric tons/ha) Average ground fuel load 3.5 tons/acre (8 metric tons/ha) All fuels are at very low loads, USA commonly 3-7 times larger Stephens 2004
How Common are Average Fuel How Common are Average Fuel Loads? Loads? Less than average load of 6.6 tons/acre (15.2 metric tons/ha) on 73% of plots Greater than 8 tons/acre (18 metric tons/ha) on 24% of plots Greater than 16 tons/acre (36.8 metric tons/ha) on 8% of plots Conclusion – average fuel loads are rare (14% of plots) – high loads in small areas, low hazard
Wildfire July 4, 2003 Wildfire July 4, 2003 • Started in chaparral below forest – In SSPM lightning ignited fires suppressed by 8 person hand crew • Very low hazards, suppression efficient • Fire burned approximately 1500 acres • Largest fire in 20 years – Occurred at end of severe drought – Same drought as in Southern California
Wildfire Impacts Wildfire Impacts • Approximately 20% of trees killed – 50% of the smallest and largest trees killed • Fire was very patchy – directly linked to heterogeneity of forest structure and fuels – Fire maintained or increased spatial heterogeneity • produces fire with diverse effects • continues high spatial heterogeneity • bark beetles killing a few trees • Mortality very low even after 4 year drought and wildfire
Forest Restoration in Similar Forests Forest Restoration in Similar Forests High amount of spatial variability desired, probably was the pre-historic landscape – can live with some areas with high fuel hazards, high snag densities Contrast: Large continues forested areas with high fire hazards – very susceptible to high severity fires Must develop methods to measure, quantify, and communicate spatial variability Currently rare in US forest management most standards and guides as for average conditions replicated at the stand level over large areas
Acknowledgements Acknowledgements Carl Skinner USFS PSW Research Station Samantha Gill Cal Poly State University Ernesto Franco Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, (CICESE), B.C., Mexico
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